The present invention relates to electromagnetically controlled switches, such as relays and contactors, and in particular to an improved controller for vacuum contactors.
Vacuum contactors are electrically controlled switches used for interrupting high power circuits. In a vacuum contactor, a pair of contacts are enclosed inside a vacuum-tight bottle. One of the contacts is fixed to an end of the bottle and the other contact may be moved by means of a bellows toward and away from the fixed contact under the influence of an electrical solenoid. The vacuum surrounding the contacts helps suppress an arc formed when a circuit is interrupted.
“Electrically-held” vacuum contactors, as the name suggests, hold the contacts in a closed position by continuously applying a holding current applied to the electrical solenoid. Typically this holding current is much less than the current used to close or pull in the contacts when the switch is actuated. “Mechanically-latched” vacuum contactors hold the contacts in the closed position by a mechanical latch, eliminating the need for a holding current. A second solenoid releases the mechanical latch when it is desired to open the contacts.
The bellows that allows movement of one of the contacts applies a biasing force on that contact that is a combination of the spring force required to flex the bellows and resist closure of the contacts and the force of atmospheric pressure across the bellows tending to move the contacts together. An external spring may be used to balance these forces with the contacts open.
This balance of forces is upset if the vacuum contactor is moved to a different altitude having a different atmospheric pressure. For this reason, it is know to provide an external spring that is replaceable or adjustable according to the altitude. Alternatively, it is known to adjust the pull-in and/or holding current of the electrical solenoid to compensate for any force unbalance. This adjustment is performed by means of a table and a set of switches that may be set by the user.
Larger vacuum bottle and contact sets may be used for greater power handling. These larger vacuum bottles require greater actuation forces that are normally accommodated by larger solenoid coils. These larger coils require different actuation currents and holding currents.
Operation of a vacuum contactor is normally mediated by a contactor controller providing regulated control of the power applied to the vacuum contactor solenoids adjusted by the user for solenoid coil size and/or altitude. Configuration of the contactor controller for different vacuum contactors and altitudes is complex and time consuming.